Dietary Fatty Acids and the Risk of Hypertension in Middle-Aged and Older Women

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1 07/14/2010 Dietary Fatty Acids and the Risk of Hypertension in Middle-Aged and Older Women First Author: Wang Short Title: Dietary Fatty Acids and Hypertension Risk in Women Lu Wang, MD, PhD, 1 JoAnn E. Manson, MD, DrPH, 1,2 John P. Forman, MD, MSc, 1,3 J. Michael Gaziano, MD, MPH, 1,4,5 Julie E. Buring, ScD 1,2,4 Howard D. Sesso, ScD, MPH, 1,4 1 Division of Preventive Medicine, Department of Medicine, Brigham and Women s Hospital, Boston, MA 2 Department of Epidemiology, Harvard School of Public Health, Boston, MA 3 Channing Laboratory and Renal Division, Department of Medicine, Brigham and Women s Hospital, Boston, MA 4 Division of Aging, Department of Medicine, Brigham and Women s Hospital, Boston, MA 5 Massachusetts Veterans Epidemiology Research and Information Center, VA Boston Healthcare System, Jamaica Plain, MA Corresponding author and reprints: Lu Wang, 900 Commonwealth Avenue East, Division of Preventive Medicine, Brigham and Women s Hospital, Boston MA 02215; phone: (617) ; Fax: (617) ; luwang@rics.bwh.harvard.edu

2 Online Supplement. Expanded Methods Section Study Population The Women s Health Study (WHS) is a randomized, double-blind, placebocontrolled, 2 2 factorial trial evaluating the risks and benefits of low-dose aspirin and vitamin E in the primary prevention of cardiovascular disease and cancer. 1, 2 A third component, β-carotene, was initially included in the trial but terminated after a median treatment of 2.1 years. 3 Written informed consent was obtained from all participants. During the course of the trial, participants received study agents and follow-up questionnaires by mail and reported the occurrence of major cardiovascular and cancer end points and risk factor information every 6 months for the first year and annually thereafter. The trial and ongoing cohort follow-up was approved by the institutional review board of Brigham and Women s Hospital, Boston, MA. From September 1992 to May 1995, a total of 39,876 female US health professionals, aged 39 years and free from cardiovascular disease and cancer (except non-melanoma skin cancer), were randomized into the WHS. Of the 39,876 women randomized, 39,310 completed a 131- item validated semiquantitative food frequency questionnaire (FFQ). For this study, we excluded 10,751 women who had hypertension at baseline, defined as having a selfreported physician diagnosis of hypertension, self-reported current systolic BP 140 mmhg or diastolic BP 90 mmhg, or use of antihypertensive treatment. Baseline systolic BP was reported as 1 of 9 ordinal categories in 10 mmhg increments from <110 to 180 mmhg, and diastolic BP was reported as 1 of 7 ordinal categories in 5 or 10 mmhg increments from <65 to 105 mmhg. We also excluded 829 women who reported implausible total daily energy intake ( 600 or 3,500 kcal/d), 21 women who provided incomplete information on the FFQ (>70 items left blank), and 41 women who had pre-randomization cardiovascular disease or cancer. After these exclusions, a baseline population of 28,100 women remained for analysis. Assessment of Dietary Fat Intake On the baseline FFQ, a commonly used unit or portion size was specified for each food item. Participants were asked how often they had consumed that amount, on average, during the previous year. Nine possible responses ranging from never or less than once per month to 6+ per day were recorded. Nutrient intake was computed by multiplying the intake frequency of each unit of food by the nutrient content of the specified portion size according to food composition tables from the US Department of Agriculture, 4 supplemented with information obtained from the manufacturers and published reports. The estimation of fat intake also took into account the types of fat or oil used during food preparation. The trans isomers contents of unsaturated fats were estimated based on the method proposed by Sacks and Willett. 5 Intake of SFAs, MUFAs, PUFAs, and trans FAs was each calculated as sum of the respective individual FAs. All FAs intake presented in the current study have adjusted for total energy intake using the residual method. 6 The FFQ used in the WHS has demonstrated reasonable validity and reproducibility as a measure of long-term dietary intake. 7 In similar cohorts of health professionals, Pearson s correlation coefficients comparing responses from

3 the FFQ with those from four 1-week dietary records spaced over a year were 0.70 for SFAs, 0.69 for MUFAs, and 0.64 for PUFAs. 7, 8 FAs intake estimated from the FFQ also correlated well with FA composition of the adipose tissue (Spearman s r=0.51 for trans FAs and 0.48 for ω3 PUFAs). 9 Ascertainment of Incident Hypertension Incident hypertension was ascertained from annual follow-up questionnaires by meeting at least 1 of 4 criteria: a new physician diagnosis of hypertension; newly initiated antihypertensive treatment; self-reported current systolic BP 140 mmhg; or self-reported current diastolic BP 90 mmhg. Women reported the month and year of hypertension diagnosis. For incident cases missing dates of physician diagnosis or defined by other criteria, time of event was assigned by randomly selecting a date between the questionnaires with and without hypertension. Individuals who developed cardiovascular disease during follow-up, the management of which may affect BP, were censored on the date of cardiovascular disease diagnosis. In health professionals, selfreported BP correlates well with measured systolic BP (r=0.72) and diastolic BP (r=0.60), 10 and the validity of self-reported hypertension is high. 11 In a random sample of WHS participants, self-reported incident hypertension was confirmed in 48 of 50 (96%) women and absence of hypertension was confirmed in 45 of 50 (90%) women through telephone interviews. Other Baseline Variables On the baseline questionnaire, women provided self-reports of age, weight and height, smoking status, alcohol intake, physical activity, menopausal status, postmenopausal hormone use, history of diabetes and hypercholesterolemia. Body mass index (BMI) was computed as body weight (in kg) divided by square of height (in m). Total alcohol intake was calculated by summing alcohol content in consumed beer, wine, and liquor. Physical activity was assessed from self-reported frequency, intensity, and duration of walking and recreational activities, and expressed as energy expenditure in kcal/week. Diabetes was defined by self-reported physician diagnosis and confirmed by telephone interview or supplemental questionnaires. Hypercholesterolemia was defined as having a physician diagnosis, self-reported total cholesterol concentration 240 mg/dl, or current treatment for high cholesterol. Data Analyses Statistical analyses were performed using SAS software (SAS Institute, Cary, NC, USA) version 9.1. Intake of FAs was divided into quintiles. Distribution of hypertension risk factors was compared across quintiles of FAs intake to identify potential confounding factors. Person-years of follow-up were calculated for each participant from randomization to the date of incident hypertension, the last day in the study, or 29 February 2007, whichever came first. After verifying the assumption of constant proportional hazard over time (p>0.05), we used Cox regression model to estimate the hazard ratio (presented as relative risk, RR) and 95% confidence interval (CI) of hypertension across quintiles of FAs intake, with the lowest quintile as the reference. Models first adjusted for age (continuous), race (white, non-white), total energy intake (continuous), and randomized treatment assignment (vitamin E, aspirin,

4 β-carotene, or placebo); then additionally adjusted for lifestyle factors including smoking (never, former, current), total alcohol intake (continuous), physical activity (continuous), postmenopausal status (yes, no, uncertain), postmenopausal hormone use (never, former, current), and several hypertension-related nutritional factors including dietary intake of calcium, potassium, sodium, and fiber (all in quintiles) (multivariable model 1); and finally adjusted for obesity-related metabolic factors that may also serve as intermediate factors linking dietary FAs to hypertension development, including BMI (continuous), history of diabetes, and history of hypercholesterolemia (both yes, no) (multivariable model 2). Analyses were further stratified by known hypertension risk factors including age (<55, 55 years), BMI (<25, 25 kg/m 2 ), smoking status (current, non-current), alcohol intake (none, any), and physical activity (<600, 600 kcal/week). Multiplicative interactions were tested using Wald χ 2 tests. We also performed several sensitivity analyses. First, we repeated all analyses with dietary FAs represented as the percentage of total energy intake; second, we considered incident hypertension using alternative definitions, such as self-reported elevated BP only, physician diagnosis or antihypertensive treatment only, or multiple indications. The results of sensitivity analyses were similar to main analyses (data not shown).

5 References: 1. Cook NR, Lee IM, Gaziano JM, Gordon D, Ridker PM, Manson JE, Hennekens CH, Buring JE. Low-dose aspirin in the primary prevention of cancer: The women's health study: A randomized controlled trial. JAMA. 2005;294: Lee IM, Cook NR, Gaziano JM, Gordon D, Ridker PM, Manson JE, Hennekens CH, Buring JE. Vitamin e in the primary prevention of cardiovascular disease and cancer: The women's health study: A randomized controlled trial. JAMA. 2005;294: Lee IM, Cook NR, Manson JE, Buring JE, Hennekens CH. Beta-carotene supplementation and incidence of cancer and cardiovascular disease: The women's health study. J Natl Cancer Inst. 1999;91: Watt B, Merrill A. Composition of foods: Raw, processed, prepared, : Agriculture handbook no. 8. Washington, DC: U.S. Department of Agriculture, US government Printing Office; Sacks FM, Willett WW. More on chewing the fat. The good fat and the good cholesterol. N Engl J Med. 1991;325: Willett W, Stampfer MJ. Total energy intake: Implications for epidemiologic analyses. Am J Epidemiol. 1986;124: Willett W. Nutritional epidemiology, 2nd ed. New York: Oxford University Press; Salvini S, Hunter DJ, Sampson L, Stampfer MJ, Colditz GA, Rosner B, Willett WC. Food-based validation of a dietary questionnaire: The effects of week-to-week variation in food consumption. Int J Epidemiol. 1989;18: London SJ, Sacks FM, Caesar J, Stampfer MJ, Siguel E, Willett WC. Fatty acid composition of subcutaneous adipose tissue and diet in postmenopausal us women. Am J Clin Nutr. 1991;54: Klag MJ, He J, Mead LA, Ford DE, Pearson TA, Levine DM. Validity of physicians' self-reports of cardiovascular disease risk factors. Ann Epidemiol. 1993;3: Colditz GA, Martin P, Stampfer MJ, Willett WC, Sampson L, Rosner B, Hennekens CH, Speizer FE. Validation of questionnaire information on risk factors and disease outcomes in a prospective cohort study of women. Am J Epidemiol. 1986;123:

6 Table S1. Multivariable relative risks and 95% confidence intervals of hypertension in the highest quintile compared to the lowest quintile of individual fatty acid intake, stratified by baseline age. Individual fatty acids Aged 39 - <55 years Aged years Saturated Fatty Acids RR (5 th vs 1 st Quintile) P, trend * RR (5 th vs 1 st Quintile) P, trend * 4:0 to 12:0 Multivariable model ( ) ( ) 0.13 Multivariable model ( ) ( ) :0 (myristic) Multivariable model ( ) ( ) 0.19 Multivariable model ( ) ( ) :0 (palmitic) Multivariable model ( ) < ( ) 0.16 Multivariable model ( ) ( ) :0 (stearic) Multivariable model ( ) < ( ) 0.04 Multivariable model ( ) ( ) 0.85 Monounsaturated Fatty Acids 16:1 (palmitoleic) Multivariable model ( ) < ( ) Multivariable model ( ) ( ) 0.82

7 18:1 (oleic) Multivariable model ( ) ( ) 0.49 Multivariable model ( ) ( ) :1 (eicosenoic) Multivariable model ( ) ( ) 0.35 Multivariable model ( ) ( ) 0.21 Polyunsaturated Fatty Acids ω3 Polyunsaturated Fatty Acids 18:3C (α-linolenic) Multivariable model ( ) ( ) 0.69 Multivariable model ( ) ( ) :5C (eicosapentaenoic, EPA) Multivariable model ( ) ( ) 0.23 Multivariable model ( ) ( ) :6C (docosahexaenoic, DHA) Multivariable model ( ) ( ) 0.21 Multivariable model ( ) ( ) 0.33 ω6 Polyunsaturated Fatty Acids 18:2C (linoleic) Multivariable model ( ) ( ) 0.86 Multivariable model ( ) ( ) :4C (arachidonic) Multivariable model ( ) ( ) 0.03

8 Multivariable model ( ) ( ) 0.77 Trans unsaturated Fatty Acids trans 16:1 (palmitoleic) Multivariable model ( ) < ( ) 0.10 Multivariable model ( ) ( ) 0.59 trans 18:1 (oleic) Multivariable model ( ) < ( ) 0.46 Multivariable model ( ) ( ) 0.17 trans 18:2 (linoleic) Multivariable model ( ) < ( ) 0.67 Multivariable model ( ) < ( ) 0.54 * Linear trends across increasing quintiles of FAs intake were tested using the median value of each quintile as an ordinal variable. Short- to medium- chain saturated fatty acids, including 4:0 (butyric acid), 6:0 (caproic acid), 8:0 (caprylic acid), 10:0 (capric acid), and 12:0 (lauric acid), were combined due to the low percentage in total fat intake and similar food sources. Multivariable model 1 adjusted for age (continuous), race (white, non-white), total energy intake (continuous), treatment (vitamin E, aspirin, β-carotene, or placebo), smoking (never, former, current), alcohol intake (continuous), physical activity (continuous), postmenopausal status (yes, no, uncertain), postmenopausal hormone use (never, former, current), multivitamin use (never, former, current), dietary sodium, potassium, calcium, and fiber (all in quintiles). Multivariable model 2 adjusted for all covariates in multivariable model 1 and additionally adjusted for BMI (continuous), history of diabetes (yes, no), history of hypercholesterolemia (yes, no).